598 research outputs found
The rotationâactivity relation of M dwarfs : from K2 to TESS and PLATO
Studies of the rotationâactivity relation of lateâtype stars are essential to enhance our understanding of stellar dynamos and angular momentum evolution. We study the rotationâactivity relation with K2 for M dwarfs, where it is especially poorly understood. We analyzed the light curves of all bright and nearby M dwarfs form the Superblink proper motion catalog that were in the K2 field of view. Using a sample of 430âM dwarfs observed in campaigns C0âC19 in longâcadence mode, we determined the rotation period and a wealth of activity diagnostics. Our study of the rotationâactivity relation based on photometric activity indicators confirmed the previously published abrupt change of the activity level at a rotation period of âŒ10âdays. Our sample, which is more than three times larger, increases the statistical significance of this finding.PostprintPeer reviewe
Optical Properties of Pentacene and Perfluoropentacene Thin Films
The optical properties of pentacene (PEN) and perfluoropentacene(PFP) thin
films on various SiO2 substrates were studied using variable angle
spectroscopic ellipsometry. Structural characterization was performed using
X-ray reflectivity and atomic force microscopy. A uniaxial model with the optic
axis normal to the sample surface was used to analyze the ellipsometry data. A
Strong optical anisotropy was observed and enabled the direction of the
transition dipole of the absorption bands to be determined. Furthermore,
comparison of the optical constants of PEN and PFP thin films with the
absorption spectra of the monomers in solution shows significant changes due to
the crystalline environment. Relative to the monomer spectrum the HOMO-LUMO
transition observed in PEN (PFP) thin film is reduced by 210 meV (280 meV).
Surprisingly, a second absorption band in the PFP thin film shows a slight
blueshift (40 meV) compared to the spectrum of the monomer with its transition
dipole perpendicular to that of the first absorption band.Comment: 6 pages, 6 figures, submitted to J. Chem. Phy
Printed Electrodermal Activity Sensor with Optimized Filter for Stress Detection
This paper presents a tiny, flexible, and low-cost all-analog approach for measuring electrodermal activity, based on the conductance of the skin. We propose a tiny, fully-printed system on flexible substrates, which guarantees flexibility and simplifies attachment to the body, and allows for detection of high stress values in form of a binary classification. A major contribution of this paper is the design of the printed hardware, including a novel way to optimize the hardware parameters, which is done via an evolutionary algorithm
The low-mass content of the massive young star cluster RCW 38
KM acknowledges funding by the Joint Committee of ESO/Government of Chile, and by the Science and Technology Foundation of Portugal (FCT), grant no. IF/00194/2015. Part of the research leading to these results has received funding from the European Research Council under the European Unionâs Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. [614922]. RJ acknowledges support from NSERC grants. JA acknowledges funding by the Science and Technology Foundation of Portugal (FCT), grant no. SFRH/BPD/101562/2014.RCWâ38 is a deeply embedded young (âŒ1âMyr), massive star cluster located at a distance of 1.7âkpc. Twice as dense as the Orion nebula cluster, orders of magnitude denser than other nearby star-forming regions and rich in massive stars, RCWâ38 is an ideal place to look for potential differences in brown dwarf formation efficiency as a function of environment. We present deep, high-resolution adaptive optics data of the central âŒ0.5 Ă 0.5âpc2 obtained with NACO at the Very Large Telescope. Through comparison with evolutionary models, we determine masses and extinction for âŒ480 candidate members, and derive the first initial mass function (IMF) of the cluster extending into the substellar regime. Representing the IMF as a set of power laws in the form dN/dM â Mâα, we derive the slope α = 1.60 ± 0.13 for the mass range 0.5â20âMâ,which is shallower than the Salpeter slope, but in agreement with results in several other young massive clusters. At the low-mass side, we find α = 0.71 ± 0.11 for masses between 0.02 and 0.5âMâ, or α = 0.81 ± 0.08 for masses between 0.02 and 1âMâ. Our result is in agreement with the values found in other young star-forming regions, revealing no evidence that a combination of high stellar densities and the presence of numerous massive stars affects the formation efficiency of brown dwarfs and very-low-mass stars. We estimate that the Milky Way galaxy contains between 25 and 100 billion brown dwarfs (with masses >0.03âMâ).Publisher PDFPeer reviewe
Fine Structure in the Circumstellar Environment of a Young, Solar-like Star: the Unique Eclipses of KH 15D
Results of an international campaign to photometrically monitor the unique
pre-main sequence eclipsing object KH 15D are reported. An updated ephemeris
for the eclipse is derived that incorporates a slightly revised period of 48.36
d. There is some evidence that the orbital period is actually twice that value,
with two eclipses occurring per cycle. The extraordinary depth (~3.5 mag) and
duration (~18 days) of the eclipse indicate that it is caused by circumstellar
matter, presumably the inner portion of a disk. The eclipse has continued to
lengthen with time and the central brightness reversals are not as extreme as
they once were. V-R and V-I colors indicate that the system is slightly bluer
near minimum light. Ingress and egress are remarkably well modeled by the
passage of a knife-edge across a limb-darkened star. Possible models for the
system are briefly discussed.Comment: 19 pages, 5 figure
Investigating 2MASS J06593158-0405277: AN FUor Burst in a Triple System?
articleFUor outbursts in young stellar objects are the most dramatic events among episodic accretion phenomena. The origin of these bursts is not clear: disk instabilities and/or disk perturbations by an external body being the most viable hypotheses. Here, we report our Very Large Telescope/SINFONI high angular resolution AO-assisted observations of 2MASS J06593158-0405277, which is undergoing a recently discovered FUor outburst. Our observations reveal the presence of an extended disk-like structure around the FUor, a very low-mass companion (2MASS J06593158-0405277B) at ~100 AU in projection, and, possibly, a third closer companion at ~11 AU. These sources appear to be young, displaying accretion signatures. Assuming the components are physically linked, 2MASS J06593158-0405277 would then be one of the very few triple systems observed in FUors.Science Foundation IrelandSTFC Ernest RutherfordMarie Curie CI
Measuring tiny mass accretion rates onto young brown dwarfs
We present low-resolution Keck I/LRIS spectra spanning from 3200-9000 A of
nine young brown dwarfs and three low-mass stars in the TW Hya Association and
in Upper Sco. The optical spectral types of the brown dwarfs range from
M5.5-M8.75, though two have near-IR spectral types of early L-dwarfs. We report
new accretion rates derived from excess Balmer continuum emission for the
low-mass stars TW Hya and Hen 3-600A and the brown dwarfs 2MASS
J12073347-3932540, UScoCTIO 128, SSSPM J1102-3431, UScoJ160606.29-233513.3,
DENIS-P J160603.9-205644, and Oph J162225-240515B, and upper limits on
accretion for the low-mass star Hen 3-600B and the brown dwarfs UScoCTIO 112,
Oph J162225-240515A, and USco J160723.82-221102.0. For the six brown dwarfs in
our sample that are faintest at short wavelengths, the accretion luminosity or
upper limit is measurable only when the image is binned over large wavelength
intervals. This method extends our sensivity to accretion rate down to ~1e-13
solar masses/year for brown dwarfs. Since the ability to measure an accretion
rate from excess Balmer continuum emission depends on the contrast between
excess continuum emission and the underlying photosphere, for objects with
earlier spectral types the upper limit on accretion rate is much higher.
Absolute uncertainties in our accretion rate measurements of ~3-5 include
uncertainty in accretion models, brown dwarf masses, and distance. The
accretion rate of 2e-12 solar masses/year onto 2MASS J12073347-3932540 is
within 15% of two previous measurements, despite large changes in the H-alpha
flux.Comment: Accepted by ApJ. 23 pages, 5 figures, 3 table
An Indacenopiceneâbased Buckybowl Catcher for Recognition of Fullerenes
A novel buckybowl catcher with an extended Ï-surface has been synthesized via cross-coupling of two bowl shaped bromoindacenopicene moieties with a tolyl linker. The obtained catcher has been unambiguously characterized by 2D-NMR and mass spectrometry. DFT calculations indicate that the curved shape of the receptor moieties is favourable for binding fullerenes. Effective binding was confirmed for interactions with C and C utilizing NMR spectroscopy and isothermal titration calorimetry (ITC). The resulting binding values show a higher affinity of the catcher towards C over C. The designed catcher demonstrated the fundamental possibility of creating sensors for spherical aromaticity
Results of 1992 seismic reflection experiment in Lake Baikal
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95684/1/eost9857.pd
On the circum(sub)stellar environment of brown dwarfs in Taurus
Aims : We want to investigate whether brown dwarfs (BDs) form like stars or
are ejected embryos. We study the presence of disks around BDs in the Taurus
cloud, and discuss implications for substellar formation models. Methods : We
use photometric measurements from the visible to the far infrared to determine
the spectral energy distributions (SEDs) of Taurus BDs. Results: We use Spitzer
color indices, Halpha as an accretion indicator, and models fit to the SEDs in
order to estimate physical parameters of the disks around these BDs. We study
the spatial distribution of BDs with and without disks across the Taurus
aggregates, and we find that BDs with and without disks are not distributed
regularly across the Taurus cloud. Conclusions: We find that 48%+/- 14% of
Taurus BDs have a circumstellar disk signature, a ratio similar to recent
results from previous authors in other regions. We fit the SEDs and find that
none of the disks around BDs in Taurus can be fitted convincingly with a
flaring index beta = 0, indicating that heating by the central object is
efficient and that the disks we observe retain a significant amount of gas. We
find that BDs with disks are proportionally more numerous in the northern
Taurus filament, possibly the youngest filament. We do not find such a clear
segregation for classical T Tauri stars (CTTS) and weak-lined T Tauri stars
(WTTS), suggesting that, in addition to the effects of evolution, any
segregation effects could be related to the mass of the object. A by-product of
our study is to propose a recalibration of the Barrado y Navascues & Martin
(2003) accretion limit in the substellar domain. The global shape of the limit
fits our data points if it is raised by a factor 1.25-1.30.Comment: 11 pages, 5 figures, A&A accepte
- âŠ